1. Field of Invention
The present invention describes a system and method for detecting chemical and or biological weapon components. The preferred embodiment is accomplished by creating two separate beams, consisting of monochromatic, coherent, polarized, quantum state entangled, exclusive or nearly exclusive co-incident photons. Then directing one beam, the probe beam, at a person or object, and analyzing the resulting conventional Raman backscatter spectrum while simultaneously directing the other beam, the detector beam, at a remote detector in order to analyze the changes in the quantum state characteristics of the entangled photons.
2. Background of the Invention
Various methodologies exist for detector technologies, for both chemical warfare and biological warfare agents. Currently, detector technology for both chemical warfare and biological warfare agents is strongest in terms of “detect to respond” or “detect to react” rather than “detect to warn.” Most only respond when the threat is directly present. Alerting civilians, first responders or troops to the immediate danger of agent exposure is often the only goal of a detector. More sophisticated or additional instrumentation further refines the nature and concentration of the danger. The efficacy of these instruments to detect and alert of imminent danger play an important part in security issues in a multitude of potential forums. One of the most challenging aspect for chemical and biological agent identification is quickly extracting the agent of interest from the other chemicals in the environment. In this aspect, however, these detector methods are often ineffective, have long standing delays in data analysis, constantly need replacement, are easily damaged or destroyed by exposure to analytes they are supposed to detect. The currently deployed detection systems require multiple platforms for detecting various biological and or chemical agents. This is complicated, expensive undertaking.
Of course, the process of screening of individuals and their belongings for potentially dangerous components is a laborious and uncertain process. Boredom and complacency at checkpoints from constant repetitive searching, along with the constant pressure to keep the line moving, can lead to breakdowns in security. For this reason, technologies capable of scanning large volumes of people from a distance have been investigated with great interest.
The accurate and specific determination for existence of chemical or biological compounds on a human subject or their belongings, without performing an invasive procedure, has several advantages. These advantages include deterring the creation, transportation or use of potentially life threatening devices, higher levels of security to individuals in large public areas, such as, airports, train stations, sports arenas and government and military facilities, and faster, safer, less invasive screening procedures. These advantages encourage usage in areas that were previously unable to be monitored, such as train and bus terminals, and increased vigilance at facilities already being monitored.
Current methodologies for screening detection are primitive at best. They are really nothing more than moving a complex laboratory out into the “field”. Representative examples of biological weapon detection techniques include:
Culturing or literally growing a colony of microbes on a nutrient containing surface (Petri-dish) and observing it with the eye or through a microscope. This is still the “gold standard” for identification of microbiological species.
Immunoassay-based detectors mimic the human body's natural immune system. Genetic-Based Detectors are another method, DNA or RNA isolated from a sample is exposed to nucleic acid sequences, or oligonucleotides, which correspond to a suspected biological agent.
Point Detectors directly examine potential biological agent-containing samples. Examples are:
Aerosol Particle Sizers (APS) in which particles are drawn through an orifice into a steady high-speed air flow.
Mass Spectrometry is another method to characterize potential Biological or chemical agents of interest by fragmenting them into progressively smaller charged pieces ending with constituent amino acid or protein pieces.
Surface Acoustical Wave Sensors are based on piezoelectric materials (those that produce an electrical current when subjected to pressure or mechanical stress) coated with antibodies or complimentary nucleic acid sequences.
Colorimetric Sensors are based on a visible color change and are, consider the fastest, cheapest, lightest and easiest type of detector to use.
Electrochemical or chemiresistor detectors, use the way electrical current changes in response to an interaction with a CW agent.
Ion mobility spectrometry (IMS) or plasma chromatography relies on small differences in the velocity of ions along a cylindrical tube, a “drift tube”, across which a constant electric field is applied.
Mass Spectrometry combined with gas chromatography is the most sensitive and most reliable technique.
Flame photometric detection (FPD), is another method where a sample is ignited in a (very small) hydrogen flame.
Photoionization detector (PID) systems use ultraviolet (UV) light to ionize (remove the most loosely held electrons) from a vapor or gas.
Isotopic Neutron Spectroscopy is a non-destructive method for the evaluation of an agent in a sealed container.
Portable Isotopic Neutron Spectroscopy System (PINS) is employed in the field to differentiate traditional munitions from those containing CW agents.
Acoustic Resonance Spectroscopy (ARS) and Swept Frequency Acoustic Interferometry (SFAI). The two related techniques, rely on the fundamental difference in the speed of sound through a solid versus a liquid.
In contrast to point detectors there is another method called Remote or Standoff Detection. The primary goal with this methodology is to create a platform which allows for both monitoring and surveillance of potential biological and chemical agents at a distance. This is similar to Cloud Recognition for weather reporting which use of Doppler radar. LIDAR is another common tool used for cloud detection and recognition and is based on the same physical principles as radar, except instead of bouncing longer wavelength radio waves off a target, higher energy light waves are used. This technology has been adapted by the U.S. Army's Long-Range Biological Standoff Detection System (LR-BSDS) which uses LIDAR-based technology to detect aerosol clouds from long distances. The Short-Range Biological Standoff Detection System (SR-BSDS) combines infrared (IR) LIDAR with ultraviolet light reflectance (UV).
Another technique unlike many discussed above is Raman Backscattering or Raman Spectroscopy. This technique can be used for scanning both objects and individuals. The underlying science involves the way in which light scatters off any surface. That is to say, when light of any wavelength impinges on a surface (or molecule), most of the scattered photons are elastically (or Rayleigh) scattered. That means that they leave with the same frequency (or wavelength) as the incident radiation. In contrast to this there is a small fraction of the scattered light (less than one in a thousand incident photons) that is inelastically (or Raman) scattered at frequencies that differ from the incident frequency by a value determined by the molecular vibrations of the sample. Raman scattering creates a discrete molecular spectrum at frequencies corresponding to the incident frequency plus or minus the molecular vibrational frequency. A Raman spectrum is thus a plot of the intensity of scattered light as a function of frequency (or wavelength). By convention, Raman spectra are shown on an orthogonal graph with the wave numbers (reciprocal centimeters) along the horizontal axis and the abscissa representing intensity or energy.
Raman spectra have long been used to determine the structure of inorganic and biological molecules, including the composition of complex multicomponent samples. Raman spectroscopy is considered to have many advantages as an analytical technique. Most strikingly, it provides vibrational spectra that act as a molecular fingerprint containing, unique, highly reproducible, detailed features, thereby providing the possibility of highly selective determinations.
In comparing Raman scattering verses other forms of analysis, the Raman approach is advantageous for several reasons:
(1) Solid, liquid and gas states can be analyzed
(2) Aqueous solutions present no special problems
(3) No special pre-scanning preparation of the sample is necessary
(4) The low frequency region is easily obtained.
(5) The device can be made inexpensive lightweight and portable
(6) Scanning can be completely non invasive and clandestine
(7) Scanning distance can be varied from centimeters to kilometers.
Several previous inventors have recognized the potential for using Raman scattering as a non-invasive (NI) sensor for scanning individuals. U.S. Pat. No. 6,574,501 discusses assessing blood brain barrier dynamics or measuring selected substances or toxins in a subject by analyzing Raman spectrum signals of selected regions in aqueous fluid of the eye. U.S. Pat. No. 5,553,616 discloses the use of Raman scattering with excitation in the near infrared (780 nm) and an artificial neural network for measuring blood glucose. WO 92/10131 discusses the application of stimulated Raman spectroscopy for detecting the presence of glucose. U.S. Pat. No. 6,070,093, describes a noninvasive glucose sensor that combines Raman measurements with complementary non-invasive techniques in order to enhance the sensitivity and selectivity of the measurement.
Other previous inventors have recognized the potential for using Raman scattering for non-invasively scanning of objects. U.S. Pat. No. 6,608,677 discloses the use of a Mini-lidar sensor for the remote stand-off sensing of chemical/biological substances and method for sensing same. U.S. Pat. No. 6,593,582 discloses a Portable digital lidar system, which in part could use raman backscattering. U.S. Pat. No. 4,802,761 dicusses Optical-fiber raman spectroscopy used for remote in-situ environmental analysis.
Still other previous inventors have recognized the potential for using entangled photons for scanning of objects. U.S. Pat. No. 5,796,477 discloses an entangled-photon microscope, for WF fluorescence microscopy.
A major challenge for all of the Raman techniques to date has been to collect spectral information with sufficiently high signal-to-noise ratios to discriminate weak analyte signals from the underlying background noise.
Existing non-invasive in vivo Raman measurements are hindered by a number of factors, including notoriously low quantum efficiency. In other words, very few inelastic scattering events occur in comparison to the number of elastic scattering events. Conventionally, in non-resonance Raman spectroscopy in order to double the efficiency of Raman scattering it is necessary to square the photon density. Unfortunately this can damage the sample. Therefore it is necessary to perform scans at either long integration times or high power densities to achieve acceptable signal-to-noise (S/N) ratios.
Other forms of Raman scattering like, resonance and surface enhancement or the combination of both can significantly improve the sensitivity and selectivity of Raman measurements. However, these enhancements are not generally applicable to all analytes or to all samples, especially in living, breathing, moving targets. Furthermore relating band intensities to analyte concentrations under such circumstances requires careful calibration procedures, which is obviously not helpful in high volume screening applications.